IPP> OPS - Ok that the 'any-value' out-of-band value hasan attribute value? [URGENT email discussion needed]

IPP> OPS - Ok that the 'any-value' out-of-band value hasan attribute value? [URGENT email discussion needed]

IPP> OPS - Ok that the 'any-value' out-of-band value hasan attribute value? [URGENT email discussion needed]

Hugo Parra HPARRA at novell.com
Wed Mar 15 13:25:03 EST 2000


Thank you Michael.  I had forgotten about tag ranges.  Following the established guidelines would certainly address my concerns.

-Hugo

P.S. -  I apologize for the HTML format of my messages.  I didn't realize the tool I'm using is doing it without informing me.  I'll look into disabling this *feature* in my tool.

>>> Michael Sweet <mike at easysw.com> 03/15/00 11:12AM >>>
[Hugo - please don't post HTML messages..]

Hugo Parra wrote:
> ...
> assumes it's a new attribute group.  But if we allow the flexibility
> that I think you're proposing, parsing an IPP packet becomes much
> more complex and dangerous.  When I run into an "unknown tag", am I
> looking at ..
> ...

But the current specs partition the tag space clearly; all tags
between 0x10 and 0xff are *value* tags, which means they will consist
of:

    tag
    name-length
    [name]
    value-length
    [value]

The tag 0x7f is used to introduce a 32-bit value tag.

For tags below 0x10, the specs show:

    0x01         = operation group
    0x02         = job group
    0x03         = end group
    0x04         = printer group
    0x05         = unsupported group
    0x06 to 0x0f = reserved for future extension groups

Based on this information a program can easily check for valid
input.

    1. 0x00 is invalid
    2. 0x01, 0x02, and 0x04 to 0x0f start a group
    3. 0x03 ends the IPP data stream
    4. 0x10 to 0x7e and 0x80 to 0xff start a value
    5. "0x7f aa bb cc dd" starts a value; the actual tag number
       is in the next 4 bytes.

Anything that doesn't follow this format can be thrown away
immediately as a bad request/response.

-- 
______________________________________________________________________
Michael Sweet, Easy Software Products                  mike at easysw.com
Printing Software for UNIX                       http://www.easysw.com
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